This chapter introduces the second volume of Psychotherapy Relationships That Work and frames its work within the Interdivisional APA Task Force on Evidence-Based Relationships and Responsiveness. The book presents clinical examples, original meta-analyses, diversity considerations, training implications, and research-infused practice recommendations for nine methods of adapting or tailoring psychotherapy to clients’ transdiagnostic characteristics (attachment style, coping style, racial/ethnic culture, gender identity, therapy preferences, reactance level, religion/spiritual identity, sexual orientation, and stages of change). The chapter outlines the purpose and history of the interdivisional task force and its relation to previous efforts to identify evidence-based practices in psychotherapy. The chapter also presents the key limitations of the work.